Electrophoretic display involves a new display technology, and it also involves a display technology capable of achieving alternate color display by the movement of charged particles via the control on presence and absence of the electric field between two plate electrodes arranged opposite to each other in accordance with the principle that the charged particles can move in the electric field.
In an EPD device, one electrophoretic unit works as a pixel; the electrophoretic units are arranged in a two-dimensional matrix to form a display plane; different grayscales or colors can be displayed by lightening or darkening the pixels as required; and plane images can be obtained with the combination of pixels. Microcup EPD devices are one type of the EPD devices and can be applied to newspapers, magazines, books, print advertisements and the like, and electronic paper (e-paper) is one of the various applications.
A microcup EPD device is manufactured by forming electrophoresis liquid by dispersing charged pigment particles in a dielectric solvent, encapsulating the electrophoresis liquid in microcups, and finally arranging the microcups between two plate electrodes (namely an electrophoretic substrate and a drive substrate). When a voltage is applied to the two plate electrodes, the charged particles will migrate between the two plate electrodes in the form of electrophoresis according to the their charge properties and the electric field direction; the movement of the charged particles is controlled by the application of appropriate voltage to each region of the plate electrode; and hence corresponding images can be generated by the display device.
Compared with the passive technology, the active matrix drive technology can achieve better control and good information display and has superior advantages in the aspects of high resolution, color display and the like. Therefore, the current high-end electronic paper mostly adopts the active matrix drive technology. Thin-film transistor (TFT) technology is the most frequently applied active matrix technology. In an active matrix drive EPD technology, the TFTs are integrated on a substrate to form a drive substrate; electrophoresis gel is disposed on an electrophoretic substrate; the electrophoretic substrate and the drive substrate are bonded to form a display panel; electrical signals of a pixel electrode are controlled by the TFTs, so that charged particles in the electrophoresis gel can be migrated/gathered on a display surface, and hence external light can be reflected or absorbed, and consequently images can be formed.
FIGS. 1 and 2 are respectively a schematic plan view and a longitudinal sectional view of a drive substrate in a traditional microcup EPD device. Each sub-pixel of the drive substrate comprises a gate electrode layer 7, a Gate Insulating Layer, an active layer, an ohmic contact layer, a source electrode layer 8, a drain electrode layer 9, a channel protective layer, and a pixel electrode layer which are disposed on a substrate 1, and comprises a via hole 10 for connecting the drain electrode layer 9 and the pixel electrode layer; the gate electrode layer 7 is connected with a scanning line 6; the source electrode layer is connected with a data line 2; and the drain electrode layer 9 is connected with the pixel electrode layer. Moreover, partition walls 5 are also disposed in regions corresponding to the data lines and the scanning lines. Longitudinal sections of the partition walls 5 are of a rectangular shape, and the transverse width of an opening portion of a microcup is d1. Aperture ratio is an important parameter of the EPD device. The higher the aperture ratio, the higher the light transmission efficiency. Therefore, the higher the reflectivity of an EPD panel, the higher the contrast. However, the above microcup structure has the defect of low aperture ratio for the microcups.
In order to achieve a higher contrast, in Chinese Patent No. CN01144631.5, a microcup structure is designed to have a wide cup rim and a narrow cup body so as to attain a higher aperture ratio, and hence the resolution of the display panel can be improved along with the improvement of the aperture ratio. However, if the cup body is too narrow, the compressive strength of the display device can be reduced.
Moreover, in order to improve the aperture ratio of microcups, Chinese Patent No. CN201886252U discloses a cup body of which the longitudinal section is of a trapezoidal shape. As illustrated in FIG. 3, in this case, the transverse width of an opening portion of the microcup is d2. Although the aperture ratio is improved to a certain degree, the compressive strength of the cup body is also reduced.
Therefore, how to not only increase the aperture ratio of the microcup in an EPD device but also not reduce the compressive strength of the microcup structure is a problem to be solved.